The goal of this protocol is to evaluate adrenomedullary and systemic sympathetic function and exercise tolerance in patients with CAH and in appropriately matched healthy controls using the above standardized cycle ergometer test. Subjects with CAH will exercise with and without doubling their morning dose of hydrocortisone to evaluate whether impairments - if present - can be corrected by a "stress dose" of hydrocortisone. We hypothesize that subjects with CAH have a reduced epinephrine reserve and impaired exercise tolerance, which can at least partially, be corrected by an increase in exogenous hydrocortisone. We will also determine whether the systemic sympathetic nervous system compensates for the adrenomedullary deficiency as observed in states of acquired adrenal insufficiency. The results of this study will increase the understanding of the physiologic interactions between adrenal cortex and adrenal medulla.